1. Field of the Invention
The present invention relates to a chainwheel, and more particularly to a chainwheel that is silent and reduces vibrations caused by a chain being turned on the chainwheel.
2. Description of Related Art
A chainwheel or a sprocket wheel that engages the holes in the links of a chain when the chainwheel is rotating is a common mechanism for power transmission. With reference to FIG. 13, a chainwheel (90) in accordance with the prior art meshes with an endless chain (80) that has a hole (not numbered) between each link (not numbered). The chainwheel (90) comprises a disk (not numbered) and multiple teeth (91). The disk has an outer edge (not numbered), and the multiple teeth (91) are integrally formed on and extend radially out from the outer edge of the disk. Multiple bottom lands (B) are formed between each pair of adjacent teeth (91) when the teeth (91) are formed. Each tooth (91) has a tooth profile (910) with a pitch point (A). The pitch point (A) of the tooth profile (910) is at the intersection of the tooth profile (910) with an imaginary pitch circle (not shown) and is a point on the tooth profile (910) that initially contacts links of the chain (80).
When the chainwheel (90) rotates, the teeth (91) will respectively fit into the holes in the chain (80) to transmit mechanical power either from the chainwheel (90) to the chain (80) or from the chain (80) to the chainwheel (90). The chain (80) comes in contact with both the pitch point (A) and the bottom lands (B) in the chainwheel (90) during operation. Noise and vibrations will be generated by the contact between the chain (80) and the chainwheel (90). When the chainwheel (90) is rotated at a high speed, the chain (80) will rapidly strike the chainwheel (90), which will cause more noise and vibrations.
The undamped noise and vibrations will be transmitted to other parts of a mechanism (not shown) that uses the chain (80) and chainwheel (90) to transmit power. For example, an exercise bike (not shown) in a gym may use a chain (80) and a chainwheel (90) to transmit physical power generated by a person's feet applying pressure to pedals of the bike to turn a wheel (not shown). However, the noise and vibrations generated by the chain (80) and chainwheel (90) will make a person riding or standing near the exercise bike uncomfortable.
To overcome the shortcomings, the present invention provides an improved chainwheel to mitigate or obviate the aforementioned problems.